Diet and Physical Activity

General information

There is lots of evidence supporting the need to have a healthy lifestyle, especially eating a healthy diet and being physically active. What you eat and how active you are can influence how you feel both physically and mentally. But we don't know much about how these factors are related. The ROOTS study is measuring diet and physical activity to investigate how they affect well-being throughout the teenage years. The information provided by ROOTS teenagers will help build a stronger evidence base for recommendations for healthy living in this age group. So, what ROOTS teenagers tell us will hopefully make a difference to teenagers in the future! In young people the benefits of physical activity are uncertain. This is partly because there is limited information available on levels of physical activity in young people, mainly due to limitations of current measurement methods and the lack of easily available and convenient methods to measure physical activity.

Contributions to the ROOTS study

Nine hundred and twenty five students took part in the detailed nutrition and activity part of the study. We tested many dimensions including:

Measuring physical activity.

This was measured in two ways:

Students wore actiheart monitors 24-hours a day over 4 days - 2 school days and a weekend so that we can compare. This measures every-day activity in every-day life (known as 'free living').

Students completed questionnaires about specific activities such as sport and less-active past-times like watching TV (this is called a 'self-report' measure)

Physical fitness

Students completed a 6-minute step-test. This allows us to estimate how efficiently the body uses oxygen to carry out physical work.

Step counts: Students wore pedometers for 7 days to measure daily step counts. This does not give us pin-point accuracy but does give us an idea of how far our students are walking on a daily basis. We can also compare week days to weekends.

Physical measures: We measured height, weight, waist circumference and body composition.

Daily eating: Students completed detailed food diaries over 4 days and a short diet questionnaire. We are interested in food intake as well as eating behaviour, so the questionnaire asks about things like whether breakfast is usually eaten, where students get their lunch from, and who they eat their evening meal with.

Some definitions:

Physical activity is any body movement using muscle work that increases the energy used by the body.

Energy expenditure is the amount of energy used by the body. It is usually measured in calories. Energy is needed for your body to keep functioning and even when you are completely still your body uses energy. Resting energy expenditure varies between individuals depending upon a variety of factors such as size and muscle mass. Energy expenditure is increased when physical activity is carried out because moving muscles need more energy. The amount that energy expenditure increases during movement depends on the amount of muscle used for the activity and the intensity of that movement.

Physical fitness includes things such as muscle strength, flexibility, balance, power and speed but also refers to how efficiently your body uses oxygen during active work/exercise. This can be assessed by measuring the amount of oxygen used by the body during an exercise test - we use a 6-minutes step test.

Exercise is usually planned physical activity done with the intention of increasing energy expenditure and/or physical fitness. Exercise involves increased physical activity and therefore increased energy expenditure. Exercise can be of different intensities and training at high intensity exercise can lead to an increase in physical fitness.